docs: def check_sparsity(x, fraction=0.6):
      '''
      check_sparsity(x) yields either x or an array equivalent to x with a different sparsity based on
        a heuristic: if x is a sparse array with more than 60% of its elements specified, it is made
        dense; otherwise, it is left alone.
  
      The optional argument fraction (default 0.6) specifies the fraction of elements that must be
      specified in the array for it to be un-sparsified.
      '''
      if not sps.issparse(x): return x
      n = numel(x)
      if n == 0: return x
      if len(x.data) / float(x) > 0.6: return x.toarray()
      else: return x